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Compositional stratification in the deep mantle   总被引:2,自引:0,他引:2  
A boundary between compositionally distinct regions at a depth of about 1600 kilometers may explain the seismological observations pertaining to Earth's lower mantle, produce the isotopic signatures of mid-ocean ridge basalts and oceanic island basalts, and reconcile the discrepancy between the observed heat flux and the heat production of the mid-ocean ridge basalt source region. Numerical models of thermochemical convection imply that a layer of material that is intrinsically about 4 percent more dense than the overlying mantle is dynamically stable. Because the deep layer is hot, its net density is only slightly greater than adiabatic and its surface develops substantial topography.  相似文献   
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The relationship between abiotic and biotic factors and the spread of the European spruce bark beetle, Ips typographus (L.), was investigated at a landscape level over a model period of 18 years in the Bavarian Forest National Park in Germany. Deadwood areas - where I. typographus - caused tree mortality of 100% - were photographed annually using Color-infrared aerial photography and digitally recorded in vector form. Thirty-two static and dynamic habitat variables were quantitatively determined using spatial pattern analysis and geostatistics from 1990 to 2007 at the landscape scale. The importance of the presence of deadwood areas for thirty-two habitat variables for the occurrence of the bark beetle was quantitatively recorded using an Ecological Niche Factor Analysis (ENFA).It was shown over a long model period that the intensity of the bark beetle infestation went through different phases over the 18-year study period. No mono-causal correlations could be found between individual habitat factors and the spread of the bark beetle over the entire model period. On the one hand, these findings underline the complexity of the system, on the other hand, this could be interpreted as a possible explanation for conclusions drawn by previous studies that differ from each other.The importance of individual habitat variables and the combinations of variables varied to different extents within these phases. An examination of the cumulative importance of the habitat demonstrated that the biological structural variables such as the distance from the site of the previous year's infestation, the area and the perimeter of the infested areas from the previous year are of great importance for the incidence of the bark beetle, but not across all years. Of equal significance for assessing the size of the area and the distance of the deadwood areas from the sites of the previous year's infestation are the size of the areas, the perimeter of the deadwood areas and the proximity index. An evaluation of the stages of forest succession showed that cumulatively, a short distance between the infested areas and the forest areas with conifers in the early stages of growth was an equally important habitat factor from 1990 to 2007. By quantitatively recording habitat factors that are significant for the spread of the bark beetle it may help predict areas that are at risk and thus to develop suitable management strategies to minimise or stop the spread and the effect of the bark beetle.  相似文献   
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Sanborn Field, an agricultural demonstration field at the University of Missouri-Columbia, has over 100 years of cropping histories and management practices implemented at this site. We examined the effect of these cropping systems and management practices on earthworm populations and microbial activity. A field experiment was conducted to characterize and quantify earthworms and to determine the microbial activity in the same selected plots. We sampled 14 plots at the site, six of which were the original plots established in 1888 with the same cropping histories and management, and eight of which had been modified over the years to accommodate changing farmer needs and scientific questions. Earthworms and soil samples were collected in the spring and fall of 1999. Aporrectodea trapezoides, Aporrectodea caliginosa, and Lumbricus terrestris were the dominant species found in this field. Lumbricus terrestris was commonly associated with the no-tillage plot at Sanborn Field. Due partly to soil moisture conditions, most of the species were found and identified during the spring. Microbial activity, as expected, was greatest during the spring. Manure, no-tillage and crop rotations that include legumes had the greatest earthworm abundance and microbial activity. In general, where no fertility treatments were added to soil or where food sources were lacking, earthworm abundance decreased significantly. The abundance of earthworms found in this field reflected the cropping history and management practices used recently and within the last 100 years. In most cases, microbial activity showed similar trends as earthworm density. However, some dynamic microbial transformations, like nitrification, do not always follow the same trend as potential soil quality biotic indicators. Earthworms, along with microbial activity, may serve as useful soil quality indicators in sustained and short-term field trials.  相似文献   
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Saliva flow induced by 6-gingerol (pungent), hydroxy-α/β-sanshools (tingling), and citric acid (sour) was measured, and the time-dependent changes in the whole saliva proteome were analyzed by means of 2D-PAGE, followed by tryptic in-gel digestion and MALDI-TOF-MS peptide mass fingerprint analysis. The proteins showing significantly decreased abundance after oral 6-gingerol stimulation were identified as glutathione S-transferase P, the heat shock protein β-1, the heat shock 70 kDa protein 1, annexin A1, and cytoplasmic β-actin, whereas prolactin inducible proteins (PIP), short palate, lung and nasal epithelium carcinoma-associated protein 2 (SPLUNC2), zinc-α-2-glycoproteins (Zn-α-GP), and carbonic anhydrase VI (CAVI) were found with increased abundance. As the effects of this study were observed instantaneously upon stimulation, any proteome modulation is very likely to result from the release of proteins from preformed vesicles and not from de novo synthesis. The elevated levels of SPLUNC2, Zn-α-GP, and CAVI might be interpreted to trigger innate protective mechanisms in mucosal immunity and in nonimmune mucosal defense and might play an important role during the initial stage of inflammation.  相似文献   
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